Simulation-based Dynamic Optimization under Uncertainty of an Industrial Biological Process

GUILLERMO A. DURAND; ANIBAL M. BLANCO; FERNANDO MELE; J. ALBERTO BANDONI

Chalkidiki

Congreso; 21st European Symposium on Computer Aided Process Engineering; 2011

Parametric uncertainty can have a great impact in the outcome of dynamic optimization of industrial biological processes, leading to sub-optimal or infeasible solutions. However, if parameters’ stochastic data is considered in dynamic optimization models, and if the handling of uncertainty is done with deterministic approaches, intractable problems arise frequently. In this work, a simulation-based approach is used to dynamically optimize under uncertainty a brewery mashing process. This technique proposes the combination of dynamic simulation with deterministic and stochastic optimizations in a two levels framework. In the inner level a deterministic optimization algorithm ignores all the random elements in the problem and obtains a deterministic optimal solution, then the dynamic simulation implements this solution handling the uncertainties while respecting the guidelines given by the optimization algorithm. This level is within an outer level where a stochastic optimization technique utilizes the information from the simulation to search the decision space systematically, trying to improve the performance of the problem. The selected case study for this work is the beer mashing process, which consists in the enzymatic degradation of the polysaccharides present in the malt. This is a fundamental step within the brewery process since the composition of the mashing wort determines the quality of the final product. The main reactions that take place in the mashing are the degradation of starch, beta-glucans and arabinoxylans into small chain fermentable and non-fermentable carbohydrates. The manipulation of the temperature profile of the batch reactor is the main mechanism to control the extent of the ongoing reactions. Since high temperatures favor the production of fermentable matter but also increases the concentration of undesirable species in the wort, the choice of an adequate temperature profile is not an obvious decision.